Production of hydrogen peroxide



Jan. 15, 1963 I T. M. JENNEY ETAL 3,073,580

PRODUCTION OF HYDROGEN PEROXIDE Filed March 20, 1961 THEDDUREI M..JzmuaY DONALD I-LPBRTER r c, a m

United States Patent (Mike 3,073,680 PRODUCTIGN F HYDRGGEN PERGXIDETheodore M. Jenney, Arlington, Mass, and Donald H.

Porter, Tonawanda, N.Y., assignors to FMC Corporation, a corporation ofDelaware Filed Mar. 20, 1961, Ser. No. 96,876 2 Claims. (Cl. 23-407)This invention relates to the production of hydrogen peroxide by thealternate reduction and oxidation of an anthraquinone working material,and more particularly to a continuous process wherein a nuclearlyhydrogenated anthraquinone is employed as the working compound.

Heretofore, the anthraquinone process has been commercially practicedwith alkylated anthraquinones, e.g., 2- ethyl anthraquinone, or mixturesof various alkylated anthraquinones. These compounds are dissolved inselected solvents, and the mixture or working solution is then subjectedto alternate reduction and oxidation. Hydrogen peroxide is producedduring the oxidation step and is separated from the remainder of theworking solution. This process is fully described in United StatesPatent 2,657,980 issued to Sprauer on November 3, 1953.

These working compounds employed by prior workers have been found to becommercially desirable because of the relative ease of carrying out thehydrogenation and oxidation steps. However, they suffer the disadvantageof rapidly degrading to products which are incapable of being cyclicallyreduced and oxidized to produce H 0 Increasing the temperature at whichthe reduction or oxidation occurs further accelerates this sidereaction, with the production of increased amounts of degradationproducts. Additionally, if the proportion of working compound which ishydrogenated per pass through the system (also termed depth ofhydrogenation) is increased, the amount of degradation rises sharply.

These conventional anthraquinone working compounds also undergo somenuclear attack during the catalytic hydrogenation step. This results inthe gradual formation of tetrahydro anthraquinone derivatives. Thesecompounds, unlike the degradation products reviewed above, will produceH 0 upon cyclic reduction and oxidation. Moreover, the inclination toform unknown degradation products which cannot be reduced and oxidizedto form H 0 appears to be greater with the alkylated anthraquinones thanwith their tetrahydro derivatives.

In spite of this, the art has not favored the conversion of theanthraquinone working compounds to their tetrahydro derivatives, or theuse of these derivatives as working compounds, because of the diflicultyencountered in commercially reducing and oxidizingtetrahydroanthraquinones to form hydrogen peroxide. This is clearlydisclosed in United States Patent 2,739,042 issued to A. E. Corey et al.on March 20, 1956. In an effort to avoid working with the tetrahydroderivative, the patentees recite a method of regenerating anthraquinonesfrom their corresponding tetrahydro derivatives. This is done by heatingthe tetrahydroanthraquinone-containing solution in the presence of adehydrogenation catalyst to convert the tetrahydroanthraquinone to itsprecursor anthraquinone. This technique is designed to minimize theamount of tetrahydroanthraquinone formed in the cyclic process byincluding special processing steps for treating the work solution duringcyclic operation.

Patented Jan. 15, 1963 Another procedure for reducing the formation oftetra hydro derivatives is taught in United States Patent 2,673,- 140.This is done by conducting the catalytic hydrogenation under verylimited pressures, and by keeping the amount or" hydrogenation (depth ofhydrogenation) to very restricted amounts.

It is an object of this invention to produce hydrogen peroxide by theanthraquinone process, employing as the working compound ananthraquinone derivative which is substantially stable, and whichresists being converted into derivatives that cannot produce hydrogenperoxide upon oxidation.

It is a further object of the invention to produce hydrogen peroxide bythe anthraquinone process wherein the amount of hydrogen peroxideproduced remains substantially constant per pass of working mixturethrough the equipment.

It is a further object of the invention to produce hydro gen peroxide bythe anthraquinone process in which a working compound is employed whichhas improved stability against the formation of degradation products athigh temperatures and under increased depths of hydrogenation.

These and other objects will be apparent from the following disclosure.

It has now been determined, quite unexpectedly, that a continuousprocess for producing hydrogen peroxide, by alternate reduction andoxidation of a tetrahydro derivative of an anthraquinone, can be carriedout efficiently and economically provided that the tetrahydro derivativeis present in amounts greater than about 85% of the working compound;that it is hydrogenated to a depth of 55 to that that it is contacted byair passed into the working solution through diffusers having porediameters from about 0.006 to 0.015 inch at a flow rate of about 2 toabout 4 c.f.m. per square foot of oxidizing tower cross-sectional area,and for a minimum contact time of about 15 seconds.

In the present process the working solution contains the tetrahydroderivative of an anthraquinone in the amount of at least about of theworking compound or compounds present. This proportion of tetrahydroderivative is required in order to obtain the full benefit of itsincreased stability. This is illustrated by the figure from dataobtained in Example '1, hereinafter described.

In the FIGURE, curve 10 represents the concentration of ethylanthraquinone (expresed as wt. percent) in the work solution during thetest. Curve 1'2. similarly represents the concentration of ethyltetrahydro anthraquinone in the work solution. As will be observedduringthe course of this test, curve 10 decreases in value, while curve 12increases. This is due to the conversion of the ethyl anthraquinone toethyl tetrahydro anthraquinone in the" work solution, until virtually noethyl anthraquinone re-. mains.

Curve 14 represents the total amount of usable anthraquinones capable ofproducing hydrogen peroxide,:

In effect, curve 14 gives the a of the runand also the amount whichremains at any point throughout the test period. Point 16, on curve 14,is the point where the ratio of ethyl tetrahydro anthraquinone to ethylanthraquinoue reaches about 85% by weight of the total anthraquinonepresent. The sharp change in the slope of curve 14, at point 16, clearlyshows the striking change in degradation rate of the working mixture,when it contains ethyl t'etrahydro anthraquinone in amounts over about85% by weight.

Anthraquinones which may be converted to their tetrahydro derivativesand utilized in the process of the present invention include 2-ethyl,2-isopropyl-, 2-sec-butyl, 2,5- butyl, 2-sec amyl, 1,3-dimethyl-,2-tertiary alcohol, the 2- methyl derivative, and others well known inthe hydrogen peroxide art.

The working solution containing the tetrahydro form of the workingcompound is subject to reduction in a hydrogenation zone in the presenceof a catalyst. The catalyst employed is most suitably a noble metalcatalyst, such as palladium deposited on an inert carrier. The carriermay comprise alumina, carbon, silica, silica alumina, calcium aluminumsilicate, carbonates and others. Reduction of the tetrahydro derivativetakes place in a fixed bed chamber. In this type of catalytichydrogenator, the catalyst is supported at the base of the hydrogenatoron a perforated holder, and working solution is passed into the top ofthe hydrogenator concurrently with excess hydrogen. This mixture isreduced by mere contact with hydrogen in the presence of the catalyst,as it flows through the fixed bed. The proportion of working compoundwhich is hydrogenated per pass (depth of hydrogenation) is at leastabout 55 to 80%. If higher depths of hydrogenation are desired, i.e. upto 90%, they may be carried out readily, but with some increase in theformation of degradation products. However, even if the instant processis operated to yield a 90% depth of hydrogenation, the build-up ofdegradation products is no greater than that obtained with conventionalanthraquinones when operated to yield 50% depth of hydrogenation.

The working solution, after leaving the catalytic hydrogenator, ispassed into an oxidizer. In the oxidizer, the working solution isoxidized by contacting the solution with air. In the normal mode ofoperation, the working solution flows continuously into the base of theoxidizing tank and is removed as oxidized overflow through a standpipeat the top of the oxidizing vessel. Air is pumped into diffusers locatedat the base of the oxidizing vessel and is released through the diffuseropenings as a continuous upward flow of dispersed bubbles passingthrough the working solution.

The oxidation of the tetrahydroanthrahydroquinones is more difficultthan corresponding hydroanthraquinones and requires the hereinafterdescribed operating conditions to carry out the oxidation on acommercial scale. The conditions under which oxidation takes place arecritical since the amount of oxidation which occurs is governed by theamount of oxygen mass transfer between the liquid phase (workingsolution) and the gaseous, or air phase. It has been found that theworking solution should be passed through the oxidizer at rates notlower than of about 400 to 600 liters per hour per foot of towercross-section in order to obtain maximum mass transfer. Flow rates belowthis amount result in substantially diminishing the mass transfer rate.Flow rates above this amount do not materially increase the rate of masstransfer per unit quantity of solution (mass transfer coefficient).

The rate of flow ofair into the oxidizer also must be controlledcarefully in order to obtain optimum oxidation of the working solution.The volume of air flowing through the oxidizer, which is generally atatmospheric pressure, although either subatmospheric or superatmospheric pressures may be employed, is maintained at be- 4, tweenabout 2 to about 4 c.f.m./ft. that is, the volume of air passing throughthe column, regardless of the pressure within the tower, must measurebetween about 2 to about 4 c.f.rn./ft. of oxidizing tower.

Contrary to what might be expected, supplying copious quantities of airinto the oxidizer does not provide high mass transfer rates. When theflow of air into the oxidizing tower is maintained between 2 to 4c.f.m./ft. of oxidizing tower, the mass transfer coefiicient (oxidationrate) becomes desirably high. When flow rates of air above this rangeare employed, an unexpected sharp decrease occurs in both the masstransfer coefficient and in the volume of liquid contained in theoxidizing vessel. The sudden decrease in the liquid volume of theoxidizer, when a given air throughput is reached, is termed the liquidholdup break-point. Air flow rates above this point can never give highmass transfer rates because of the great decrease in volume of workingsolution present in the oxidizer.

When the rate of flow of air into the oxidizer is employed at below 2c.f.m./ft. of oxidizing tower, the mass transfer coefficient again dropsoff quite considerably. As a result, oxidation of the working solutionis incomplete and requires additional passes through the oxidizer tocomplete the oxidation.

The size of the air bubbles which are released by the difiusers andwhich contact the working solution must also be subject to carefulcontrol. If extremely fine air bubbles, i.e. those obtained by employingdiffusers having an average pore diameter below 0.005 are employed,small mass transfer coefficients are obtained. The finer air bubbleswhich are released by the smaller diameter diffusers appear to create anextremely stable foam in the oxidizing vessel. As a result, there isvery little effective agitation and, consequently, a serious diminishingof mass transfer coefficient.

Additionally, the finer air bubbles cause the liquid holdup break-pointin the oxidizing unit to be reached sooner; that is, the liquid holdupbreak-point is reached at a .lower air flow than with coarser-sized airbubbles. Accordingly, the maximum air flow rate of finer air bubbleswhich can be passed through the oxidizer before reaching the liquidholdup break-point is low. This prevents greater volumes of air fromeffectively contacting the working solution.

It has been found that diffusers having an average pore diameter of from0.006 to 0.015" deliver air bubbles which give maximum mass transfercoefficients at air flows between 2 c.f.m. to 4 c.f.m./ft. of oxidizingtower crosssectio-n. An optimum pore diameter is between 0.008 to 0.011.It diffusers having an average pore diameter above these values areemployed, incomplete oxidation occurs and lowering of the mass transfercoefficient results.

In order to obtain sufficient duration of contact between the air phaseand the working solution, or liquid phase, it has been determined thatthe height of a single-stage oxidizing tower should be at least aboutinches tall. This height permits a contact time of at least about 15seconds. Single-stage oxidation towers below this height do not allowsuflicient time for the working solution and air phase to reactcompletely. This results in erratic oxi dation and inefficientoxidation, along with decreased hydrogen peroxide production.Multi-stage oxidation towers may be employed, provided that they permitthe. air phase to contact the workingsolution for a minimum totalcontact time of 15 seconds.

After the working solution is removed from the oxidizer, it is subjectedto a water wash which dissolves the,

hydrogen peroxide in the aqueous phase. This aqueous phase containingthe hydrogen peroxide is then separated from the residual workingsolution and sent to purifying units. The residual working solution isthen recycled to the catalytic hydrogenator.

The instant process, because of its extremely stable working compound,i.e. tetrahydroquinones, has many advantages over the prior workingcompounds. Among these is the ability to operate at higher temperatureswith out deleterious side effects. By increasing the temperature ofoperation, greater quantities of working compound can be dissolved inthe working solution. As a consequence, more hydrogen peroxide isobtained per pass through the system.

Another advantage resides in the virtual elimination of quinoneregeneration steps or, alternatively, in steps for removal of degradedby-products. The tetrahydro derivatives employed as the workingcompounds have such in creased stability compared to their precursoranthraquinones that the amount of degraded by-products is materiallyreduced. As a result additional process steps are not required forremoving these by-products.

Another advantage resides in the high concentration of peroxide which isformed in the working solution. This may be attributed either to theincreased temperatures of operation or to the increased depth ofhydrogenation of the working solution. That is, more working compound isalternately reduced and oxidized per pass through the system due to anincreased depth of hydrogenation, or alternately by dissolving moreworking compound in the working solution at the higher operatingtemperatures. The increased quantity ofworking compound passed throughthe system produces more hydrogen peroxide per unit of working solution.This results in an increase in peroxide concentration in the worksolution. Upon aqueous extraction of the work solution, the increasedamounts of peroxide are absorbed in the aqueous phase resulting in anaqueous extract having a higher concentration of peroxide.

Increased peroxide concentration in the aqueous extract is extremelydesirable. It is advantageous because higher concentrations of peroxidein the aqueous phase permit more eflicient extraction. Furthermore, itreduces the amount of distillation required to purify the hydrogenperoxide product. As a result, the distillation step can be simplifiedand the time required for distillation can be reduced.

The following examples are given to illustrate the invention but are notto be considered as being limitative of it.

EXAMPLE 1 The following run was made under total recycle conditions inthe hydrogenator as described below in order to compare the degradationrate of 2-ethyl anthraquinone and Z-ethyl tetrahydroanthraquinone. Thisrecycle test accelerates reaction conditions in the hydrogenator, andcan be used to determine rapidly the rate at which working compoundswill be converted into unuseable anthraquinone derivatives by thecatalyst.

A fixed bed hydrogenator was charged with a catalyst comprising 1.0%palladium on an activated alumina carrier, and having a particle size of-20 mesh. A total of 2.5 liters of a work soluion comprising 61 wt.percent dimethylnaphthalene as the quinone solvent and 39 wt. percenttrioctylphosphate as the hydroquinone solvent was passed downwardlythrough the hydrogenator with excess hydrogen at a pressure of 35p.s.i.a. and at a temperature of 50 C. The original solution containedan anthraquinone composition indicated in Table I. The

Table I Useable Anthraquinone Composition (Wt. Percent) Time (Hrs.)

2'Ethy1 Z-Ethyl Total Anthraqui- Tetrahydronone Anthraquinone EXAMPLE 2The following runs were made to compare the rate of degradation ofZ-ethyl tetrahydroanthraquinone with its precursor non-nuclearhydrogenated compound, 2-ethyl anthraquinone, using the process of thepresent invention.

In these tests the fixed bed hydrogenator was charged with a catalystcomprising 0.3% palladium on an activated alumina carrier, and having aparticle size of 8-14 mesh. A total of 3000 liters of working solutionwere used in each of the runs. The solvent used in the Working solutioncomprised 61 wt. percent dimethylnapththalene as the quinone solvent and39 wt. percent trioctylphosphate as the hydroquinone solvent andcontained the same amount of Working compounds in each of the runs. Thecomposition of the working compound is given in Table II.

The working solution, which is composed of the working compoundsdissolved in the working solvents, was passed downwardly through thefixed bed, along with excess hydrogen, at a temperature of 40 C. Therate at which the working solution passed through the hydrogenation, aswell as the depth of hyrogenation, is given in Table II. Of this totalflow, a fraction was recycled directly to the top of the catalyticchamber, while the remainder was passed on as forward flow to theoxidizing tower. The rates of recycle and forward flow are given inTable Ii. The working solution was maintained in the oxidizing tower atthe heights listed in Table II, and at temperatures between 40-50 C. Theoxidizing tower, which has a cross-section area of 1.33 feet, had0.008-inch pore diameter candles at the base of the tower for theadmission of air into the working solution. Air was pumped into the baseof the oxidizer at the rates lisited in Table II and passed upwardthrough the solution where it oxidized the hydrogenated workingcompounds. In each of the runs the amount of catalyst was adjusted sothat gm. moles/hour of hydrogen peroxide were obtained, and a directcomparison of the degradation rates could be made. The resultingdegradation rates are given in Table II. Also listed in Table II is theamount of residual hydroquinone compound which was not oxidized in thetower.

,T' Table II Runs 1 2 3 4 5 Solution Composition, gm. Molcs/ Liter:

2 Ethyl Anthraquinone 0. 45 0. 45 0. 05 0.05 0. 05 2-Ethy1Tctrahydroanthraquinone .1 0.05 0.05 0. 45 0. 45 0. 45 Total Flow inHydrogcnator Hr 11,000 7,537 11.000 7,337 0,110 Recycle Flow toHydrogcna rsl 10,000 5.070 10.000 0,070 5, 550 Forward Flow to Oxidizcr,Liters/ Hour Ft. 750 500 750 500 416 Temperature of Hydrogenation, C. 4040 40 4O 40 Depth oi Hydrogenation, Pcrccnt 50 75 5O 75 90 Air Flow Ratein Oxidizcr, mm..." 3 3 3 3 3 Air Efficiency, Percent 80 80 80 80 80Height of Working Solution in Oxidizcr, Ft 20. 23.8 29.1 25. 5 20. 5H2O: Produced, gm. Moles/Hour 100 100 100 100 100 H2O; Concentration,gm. Molcs/ Liter 0. 25 0. 375 0. 25 0. 375 0. 450 Outlet UnoxidizedWorking Compounds, gm. Moles/Liter 0. 0025 0. 0025 0. 0025 0. 0025 0.0025 Loss of Working Compound m.

Moles/Hour Or 46 O. 92 0. l0 0. 0. 50

T able Ill EXAMPLE 3 Days of Operation 1O 10 9 10 A fixed bedhydrogenator was charged with 160 liters of a catalyst comprising 0.3%palladium on an alumina on c mpositiomwt. Percent: carrier, and having aparticle size of 8-l4 mesh. A total gi g t ifgggi 941 5 7 7 of 3000liters of work solution was employed in this run. none 1.5 5.0 s. 0 8.3The solvent used in the working solution comprised 61 5,400 5 400 4 4005 400 wt. percent dimethylnaphthalene as the quinone solvent igs gg g fito Hydmgenator, 5 C00 5 000 4 000 r G00 and 39 wt. percenttrioctylphosphate as the hydroquinone r k F 51};555 535557 l Hour 400400 400 400 i-"ilili 2i? m t 2 t2 t2 1 s 1n a e ep 0 rogena on ercen 5 YTemperatur oroxidanoii, 0 Z5 44 is 44 The working solution, which iscomposed of the worlt- Air Flow Rate in oxidizer, Mm 4 4 4 4 ingcompounds dissolved in the working solvents, was %if fi fii ffgi zg ggk- 80 80 80 80 passed downward through the fixed bed along with excessOxidizcr s, Ft 30.5 30.0 00.0 30.0 hydrogen at the temperature listed inTable III. The g8; ai ifirgg f 81 84 73 69 rate at which the workingsolution passes through the L i te r n k n 0.237 0.247 0.228 0.203hydwsenawr, as well as the depth of hydrogenation, is im mae giif.iiinestiiefififffI- .0o5 .013 .016 .009 given in Table III. Of this totalflow, a fraction was regf gggi g fig ag fi g lgxg 0 02 0 02 0 01 cycleddirectly to the top of the catalytic chamber, 2 2p while the remainderwas passed on as forward flow to What is 01 aime d 4 l g 2 g Y g fif ofrecycle and forward 1. In the continuous method of producing hydrogen0;} l re 1S 6 f 6 d peroxide by alternate reduction and oxidation of aliquid h 1 132 21 3 0M 111113 Towers Warez emplole eachoof work ngsolution containing an alkylated anthraquinone l 16 a CYOSS'SBOUOII L0 yhad workmg compound, the improvement which comprises lnch pore diametercandles at the base of the tower for 5G employing a tetrahydroderivative of an alkylated anthrathe admission of air into the workingsolution. A1r was qumone in said working compound in an amount greaterpumped into the base of the oxidizers at the rates listed than about 85%by weight of said total working comin Table III, and passed upwardlythrough the solution Pound, P g Said Working Compound iIltO a ly icwhere it oxidized the hydrogenated working compounds. hyiimgenatori y gfg Said working compound to The amounts of hydrogen peroxide produced arelisted in if :23 to 1 z f c r f yi P 2 Said work- Table III. Thedegradation rates of the working comwgrkin E23 0 :2 gg i Bald pounds arelisted in Table HI, along with the amount of g i passe 8 solutlon fromresidual h dro uinonc com ound which was not oxidized diffuses havingpore dlameters from about 0'006 to n th t Ye q P r 0.015 inch at a flowrate of from 2 to 4 c.f.m./ft. of 1 The ow rs. f d f t 1 f 39 d dcrosssectron of the oxidizing zone, said air and working ese runs werecon mile or a 0H1 Y compound having a rmnimum contact time of about 15mg which periodic analyses of the working compound seconds, separatingthe hydrogen peroxide produced durwere made. The changes found in thecontent of working ing the oxidation step from said working compound,recompounds are listed in Table 1 1 cycling the working compound foradditional processing Pursuant to the requirements of the patentstatutes, the to the a y ic hydrogenator, and recovering thehydroprinciple of this invention has been explained and exg plenroxlde 2q emplified in a manner so that it can be readily practiced is l g fg fg i fi f the workmg compound by those skilled in the art, suchexemplification including y aqmnone' what is considered to represent thebest embodiment of References Cited in the file of this patent theinvention. However, it should be clearly understood UNITED STATESPATENTS that, within the scope of the appended claims, the inven- 2 158525 Rled et a1. May 16, 1939 tron may be practiced by those skilled inthe art, and 2,836 416 Cox et a1 Ma 12 1959 having the b nefit of thisdisclosure, Otherwise than as 2,966,398 Jamey l: 1960 specificallydescribed and exemplified herein. 2,995,424 Farrell Aug. 8: 1961

1. IN THE CONTINUOUS METHOD OF PRODUCING HYDROGEN PEROXIDE BY ALTERNATEREDUCTION AND OXIDATION OF A LIQUID WORKING SOLUTION CONTAINING ANALKYLATED ANTHRAQUINONE WORKING COMPOUND, THE IMPROVEMENT WHICHCOMPRISES EMPLOYING A TETRAHYDRO DERIVATIVE OF AN ALKYLATEDANTHRAQUINONE IN SAID WORKING COMPOUND IN AN AMOUNT GREATER THAN ABOUT85% BY WEIGHT OF SAID TOTAL WORKING COMPOUND, PASSING SAID WORKINGCOMPOUND INTO A CATALYTIC HYDROGENATOR, HYDROGENATING SAID WORKINGCOMPOUND TO AT LEAST 55 TO 75% OF ITS TOTAL CAPACITY, PASSING SAIDWORKING COMPOUND INTO AN OXIDIZING ZONE, CONTACTING SAID WORKINGCOMPOUND WITH AIR PASSED INTO THE SOLUTION FROM DIFFUSERS HAVING POREDIAMETERS FROM ABOUT 0.006 TO 0.015 INCH AT A FLOW RATE OF FROM 2 TO 4C.F.M./FT2 OF CROSS-SECTION OF THE OXIDIZING ZONE, SAID AIR AND WORKINGCOMPOUND HAVING A MINIMUM CONTACT TIME OF ABOUT 15 SECONDS, SEPARATINGTHE HYDROGEN PEROXIDE PRODUCED DURING THE OXIDATION STEP FROM SAIDWORKING COMPOUND, RECYCLING THE WORKING COMPOUND FOR ADDITIONALPROCESSING TO THE CATALYTIC HYDROGENATOR, AND RECOVERING THE HYDROGENPEROXIDE SO PRODUCED.